concurring in part:
I agree with the majority’s conclusion that “[n]o authorization for exchanges of state lands exists in the Arizona Constitution,” and for that reason I concur in the holding that the exchange statutes are unconstitutional as applied to school trust lands. I do not, however, agree with the reasoning utilized by the majority to reach that result, and for that reason, I write separately.
1. An Exchange is Not a “Sale” Authorized by the Constitution.
I disagree with the majority’s conclusion that because an exchange is based on an appraisal establishing a monetary value, it is a “sale” within the meaning of art. 10, § 3 that requires a public auction. Fain has pointed out similar situations in which courts have distinguished between exchanges and sales. See, e.g., Watson v. Caldwell, 160 Fla. 398, 35 So.2d 125 (1948). The semantic battle over the meaning of the word “sale,” however, is not, in my opinion, dispositive of this issue.
The best indication that an exchange is not a “sale” in the constitutional context of article 10 is that exchanges were not allowed as “sales” under the 1910 Enabling Act until it was amended in 1936 to include them. Implicit in that amendment is a recognition by Congress that the Enabling Act of 1910 did not allow exchanges. The Arizona Constitution, which contains substantially identical wording to the 1910 Enabling Act, and which has not been amended to conform to the 1936 amendment to the Enabling Act, therefore also does not allow exchanges. Further persuasive indication that the Arizona Constitution would have to be amended in order to explicitly authorize exchanges is found in the fact that both North Dakota and Montana have amended their constitutions to allow exchanges after being given federal authority to exchange trust lands. 6 Neither of those states chose simply to recognize exchanges as constitutionally authorized under the rubric of “sales,” and neither requires public auctions for exchanges of state land.
Given this background, I do not believe that exchanges can logically be included in a constitutional definition of “sales.” Because the constitution limits disposal of state lands to those methods provided in both the Enabling Act and the Constitution, if an exchange is not a “sale,” and is not otherwise provided for in the constitution, the legislature had no constitutional authority to enact the statutory scheme providing for exchanges in A.R.S. §§ 37-604 through 37-607, as applied to school trust lands. No provision of article 10 of our constitution authorizes exchanges. Furthermore, art. 10, § 1 clearly requires that state trust land is to be disposed of only as provided in both the constitution and Enabling Act. Authorization for exchanges in the Enabling Act alone, without analogous authorization in the constitution as well, is simply inadequate. See Deer Valley. The legislature therefore was not empowered to *599enact the challenged legislation. I believe this is the crux of the constitutional issue in this case.
2. An Exchange is Not an “Other” Disposal or Disposition Authorized by the Constitution.
Fain also argues, however, that even if exchanges are not included within the constitutional meaning of “sales,” they are authorized by the constitutional language referring to “other disposal” or “any disposition” in various sections of article 10. This argument is again contradicted by the fact that the 1910 Enabling Act did not allow exchanges as either “sales” or as any “other” disposal or disposition, as evidenced by its subsequent amendment in 1936 to include them. • A more logical explanation of the meaning of these constitutional references to “other” disposals or dispositions is derived by examining the overall scheme of both the 1910 Enabling Act and the Arizona Constitution. For example, the Enabling Act referred to “the use thereof of the natural products” of the lands granted. Arizona Enabling Act, Ch. 310, § 28, 36 Stat. 557, 574 (1910). Disposition of “other products” is also mentioned in art. 10, § 3, which requires notice by publication for “any sale or contract for the sale of any timber or other natural product of such lands.” Additionally, art. 10, § 4 refers to “timber, and other products of land” in its appraisal requirement. The legislature has provided for “disposition of products of state lands” by requiring that sale of “timber products, stone, gravel, and other products and property upon lands belonging to the state” must conform to both the Enabling Act and the constitution. See A.R.S. § 37-481. The Attorney General opined in 1979 that dispositions of these products, other than by sale of the land, were not subject to the public auction requirement of art. 10, § 3, but could not be disposed of for less than their appraised value. Op.Ariz.Att’y Gen. 179-166. Given this background, it appears that constitutional references to “other” disposals apply to disposals that involve less than a fee simple interest in the land. I therefore would not infer a constitutional authorization of exchanges, which result in a transfer of a fee simple interest, from the constitutional references to “other” disposals or dispositions.
I conclude that although the exchange statutes are authorized by the amendments to the Enabling Act, they are not constitutionally authorized. The legislature therefore had no authority to enact a statutory scheme providing for exchanges of state school trust lands; thus, those statutes are void.
3. Effect of the Majority Decision.
The majority notes that the attorney general has phrased the issue in this case as follows:
May the state enter into exchange transactions without complying with the public auction requirement of the Arizona Constitution when the transaction is permitted by state statutes passed under the authority of the Enabling Act?
The majority relies in part on this court’s decision in Deer Valley in answering this question in the negative. However, I would not so literally apply some of the broadly worded language of Deer Valley to the issues raised in this case. For example, Deer Valley holds that the constitution “plainly says that the state may not sell, lease, or otherwise dispose of school trust land other than to the highest and best bidder at a duly advertised public auction. Ariz. Const, art. 10, §§ 3-4.” 157 Ariz. at 540, 760 P.2d at 540 (emphasis added). However, a “plain” reading of sections 3 and 4 of article 10 indicates that public auction is required only for the “sale or lease” of state trust lands, while an appraisal is required for “sale or other disposition.” To the extent that the Deer Valley decision conflates sections 3 and 4 into an unjustifiably broad requirement that public auction is required for all disposals of land, not just sale or lease, I do not believe it is supported by the plain language of article 10.
Under my analysis that an exchange is not a “sale,” therefore, if an exchange were otherwise constitutionally authorized by amendment, it would not require a pub-*600lie auction under the present wording of article 10. Under the majority’s analysis, however, because an exchange is a “sale” that is already constitutionally authorized, all that would be necessary to remedy the constitutional infirmity of the present statutory scheme would be for the legislature to reenact the exchange statutes with the requirement that a public auction be held before an exchange could be made. Such a statutory enactment would render the exchange statutes in compliance with the requirement that “sales” be made only after public auction, and no constitutional amendment authorizing exchanges would be necessary. I contend that this leads to an absurd result: the requirement of holding a public auction for an exchange is impossible to implement.
When the state agrees to exchange land with a private party, it does so for a specific purpose relating to the unique nature of the land it wishes to acquire, not for the general purpose of obtaining the highest monetary equivalent for the land, as is the case with a sale. Thus, to require the state to forego a desirable exchange of state land for a specific private parcel with a unique benefit to the state because some other private party has offered an exchange of private land with a higher appraised monetary value would be to defeat the specific purpose of an exchange. It would force the state, in every instance, to first sell its own land at public auction, and then attempt to purchase, with the proceeds from that sale, the specific property it would have attempted to obtain by exchange. In a purchaser role, the state’s bargaining position with the seller of the property that the state hopes to obtain may not always be as advantageous as if the state were able to exchange specific land in return. An exchange by public auction is an oxymoron, certainly not within the intentions of the framers of either the 1910 Enabling Act or our constitution.
This court has previously held that these provisions should be “reasonably construed, in view of the object of the grant, and the purpose of the restrictions.” State ex rel. Conway v. Land Department, 62 Ariz. 248, 254, 156 P.2d 901, 903 (1945). I would reasonably construe the constitution to conclude that an exchange is not a “sale,” and is not otherwise constitutionally authorized. What is needed is a constitutional amendment authorizing exchanges, not a statutory requirement of public auction to validate the challenged legislation.
4. Effect of Statutory Provisions Regarding Sales.
I am also concerned about how the majority decision will affect the scope of other statutory provisions. If exchanges are constitutionally categorized as “sales,” do the statutes applicable to “sales” now apply to exchanges? For example, “void sales” are statutorily provided for as follows:
A sale made by mistake or not in accordance with law, or obtained by fraud, is void and the certificate of purchase issued thereon is void. The holder of the certificate shall surrender it to the state land department. The department shall, except in case of fraud, refund the money paid thereon to the holder of the certificate, and make compensation to the holder for the actual value of the improvements placed on the land by the purchaser. The value shall be determined by the department and paid from the general fund.
A.R.S. § 37-249. The majority’s conclusion that today’s decision applies only prospectively from the date of the mandate in Deer Valley does not suspend the operation of this statutory remedy for a void sale, because that issue is not even addressed in the context of this case, which involves an incomplete transaction. If an exchange is not a sale, however, the above statute voiding completed transactions would not apply to past exchanges, and this issue would not need to be resolved.
5. Retroactivity Analysis.
Fain points out that since 1971, when the legislature first enacted the statutory scheme allowing these exchanges, “30 such exchanges have been completed involving nearly 170,000 acres of land.” Fain also correctly points out that “the validity of *601these past exchanges is not directly before the Court.” Other than brief references to past transactions, the parties in this case did not brief the issue of retroactive application of a holding that exchanges are unconstitutional. Additionally, the Deer Valley decision did not address the issue of its own retroactive application.
Neither this case nor Deer Valley presents a retroactivity issue, because neither case involved a completed exchange. In this case the court is not presented with the question whether to undo any previous exchange, because the Department did not approve Fain’s application; thus, no exchange occurred. In Deer Valley, the superior court dismissed the school district’s action to condemn a proposed school site; this court merely affirmed the trial court’s dismissal of the action, and also did not need to address the voidness of a land transaction completed in reliance on an invalid statutory scheme.
Because the issue of the retroactivity of today’s decision is not directly before this court, I would not address it until a case arose involving interested parties who could authoritatively argue the issue. Alternatively, if the majority must address the issue in the context of this case, I would have preferred ordering supplemental briefing from these parties on the specific issue of retroactivity. However, I will comment on the retroactivity issue because the majority has chosen to decide it.
I do not necessarily disagree with the majority’s retroactivity analysis utilizing the 3-prong test from Chevron Oil, adopted by this court in Chevron Chemical, to conclude that, although the exchange statutes are unconstitutional, our decision today will be applied only prospectively. The majority’s analysis that an exchange is a “sale” is clearly a new and novel constitutional interpretation that could hardly be foreshadowed by prior case law. The retroactivity cases cited by the majority, however, deal largely with common law principles that have been changed by judicial decision.
My concern is that such a retroactivity analysis does not appropriately apply to my conclusion that the statutory scheme is unconstitutional under the clear language of the constitution. My conclusion that an exchange is not a sale involves no new interpretation or overruling of prior precedent. A prospective application of a holding that a statute is unconstitutional on the basis of the clear wording of the constitution, in effect, results in this court’s suspension of the constitutional limits on the disposal of state land from 1971 to 1988, when the Deer Valley case was decided.
However, I too believe that there is authority to reach the conclusion that today’s decision should be applied prospectively, for several reasons. First, although the constitution provides that disposals made in violation of the Enabling Act shall be “null and void,” it does not so provide for disposals that comply with the Enabling Act but violate the constitution. Thus, although we must void the legislation, we are not constitutionally compelled to void all transactions that occurred in reliance on that legislation.
Second, a prospective-only application based on reliance on an unconstitutional statute is supported by other cases in which great economic harm could occur to the state from a retroactive application. This court has recognized that, at common law, a declaration of unconstitutionality had complete retroactive effect; however, the rule that an unconstitutional statute was void from its inception and thus conferred no operative rights “has been considerably eroded with time, ... and is not the law in Arizona.” Shreve v. Western Coach Corp., 112 Ariz. 215, 217, 540 P.2d 687, 689 (1975) (refusing to follow the “Blackstonian view” set forth in Norton v. Shelby County, 118 U.S. 425, 442, 6 S.Ct. 1121, 1125, 30 L.Ed. 178 (1886)). This court has also recognized that citizens are entitled to rely on the validity of a statute until its repeal or a judicial declaration of its unconstitutionality. For example, we have held that an appellant who relied on a vetoed law before the veto was found unconstitutional could not be liable for monies that would have been due had the law been in effect, because “it would be the height *602of injustice for the state to penalize ... one of its citizens for obeying a law which on its face was adopted in a constitutional manner, but which was, after such obedience by the citizen, held to be unconstitutional.” Texas Co. v. State, 31 Ariz. 485, 502, 254 P. 1060, 1065 (1927). In a later case, this court relied on that reasoning to conclude:
However desirable the total nullity doctrine of Norton may be from the standpoint of symmetrical jurisprudence it does not conform to reality. For a statute, until legislatively or judicially excised, is an operative fact which cannot be ignored. This court presumes every legislative act constitutional and indulges in every intendment in favor of its validi-ty____ No penalties should be visited upon the citizenry for doing likewise.
Austin v. Campbell, 91 Ariz. 195, 203, 370 P.2d 769, 775 (1962).
Although these cases involved whether a citizen who relied on an unconstitutional law should be penalized by criminal or civil prosecution for that reliance, I believe the reasoning applies analogously to this situation, where participants in at least 30 land exchanges relied on the provisions of the exchange statutes that are presumed to be valid until this court holds otherwise. To subject those transactions to cloudy titles on the exchanged land or to require the participants to reverse the exchanges after a period of time would be to penalize everyone involved in transactions that were meant to benefit the state.
The retroactivity analysis used in several older cases involving the validity of taxing statutes or regulations can be applied to this situation, where the challenged statute is clearly defective and is not the result of a novel judicial interpretation. In one case, this court found that a taxing practice constituted a “willful, systematic and intentional violation of the law”; however, because the court also found that the remedy of refunding appellant’s and similar claims “threatens the financial solvency of many taxing units of the state, particularly those in rural and undeveloped areas,” the court concluded it could make its decision prospective in application “where great hardship will result if caused from long continued failure to exert a legal right.” Southern Pacific Co. v. Cochise County, 92 Ariz. 395, 406, 377 P.2d 770, 778 (1963). The court pointed out that appellant’s “non-action” in delaying to seek discontinuance of a settled practice “culminates in the present threat to the existence of government itself. The State’s grace does not extend to its own destruction.” Id. As a result of the “great economic hardship” to the state, the court refused to apply the decision retroactively.
In a later case, the court of appeals applied this analysis to its holding that a property valuation system of assessment was illegal and unconstitutional. See Bade v. Drachman, 4 Ariz.App. 55, 417 P.2d 689 (1966). The court declined to make the decision prospective only, reasoning as follows:
If we were modifying or overruling a previous judicial decision, or if we were ordering a complete revampment of the assessment rolls, a process that would require substantial time to accomplish, this request [for prospective application] would have some merit. We are doing neither____ When the rights of a taxpayer are established by explicit statutory law, as in this case, we question our authority to deny or postpone relief, unless the financial stability of the taxing body is threatened with destruction as in the Southern Pacific case. We are not convinced that the granting of relief to the taxpayer in this case will substantially impair the financial integrity of either this, county or this state.
Bade, 4 Ariz.App. at 69-70, 417 P.2d at 703-04 (emphasis added).
I would apply these standards to this case. However, without further briefing by adversely affected parties, I find it difficult to determine the exact extent of economic harm that would occur to the state or other parties by retroactive application of today’s decision. But if we must decide the retroactivity issue here, I would concede that we could take notice of the significant adverse economic repercussions that *603would result if the state were required to undo the exchanges and redo them as sales to the public with the requisite public auctions, assuming that anyone would, or procedurally could, bring an action to cause such chaos. Based on this potential great economic hardship, I would hold that today’s decision applies only prospectively. Although I do not agree that the decision should run from the date the Deer Valley decision was mandated, that distinction makes no practical difference in light of the fact that the Land Department has suspended all exchanges since Deer Valley was decided.
6. Other Issues.
I agree with the majority that the 1936 amendments to the Enabling Act do not effectively amend the Arizona Constitution, and that the Enabling Act does not preempt the Arizona Constitution because it does not forbid anything that the constitution allows. I therefore concur in the result reached by the majority.
. Four years before the 1936 Exchange Amendment, Congress authorized North Dakota, Montana, and Washington to exchange state trust lands. See Act of May 7, 1932, Pub.L. No. 124 (Ch. 172), 47 Stat. 150. North Dakota and Montana both subsequently amended their state constitutions to provide for exchanges. See N.D. Const, art. IX, § 6 ("Any of said lands and any other lands controlled by the board of university and school lands, including state coal mineral interests, may, with the approval of said board, be exchanged for lands and coal mineral interests of the United States, the state of North Dakota, or any county or municipality thereof as the legislature may provide____”); Mont. Const, art. X, § 11 (“Any public land may be exchanged for any other land, public or private, which is equal in value, and, as closely as possible, equal in area.”)